1. Field of the Invention
The invention relates to a method and apparatus for measuring and monitoring osteoporosis in an animal or human patient. More particularly, the invention uses an electromagnetic field to non-invasively measure impedance changes in a bone as a monitor of osteoporosis.
2. Description of the Prior Art
Osteoporosis is a condition characterized by a loss of bone mass. It can result because of a variety of causes that include chronically restricted calcium intake, hyperparathyroidism, hypersteroidism, immobilization, and weightlessness. Lay people also associate osteoporosis with the aging process. Various prior art x-ray techniques are of some assistance in detecting a loss of bone mass. However, no safe, inexpensive, non-invasive technique is taught by the prior art to regularly monitor osteoporosis.
The present invention uses an electromagnetic field to non-invasively measure impedance changes in a bone as a monitor of osteoporosis. As will be discussed in detail subsequently in this application, Applicants have related the impedance change in a bone with bone mass loss associated with osteoporosis. U.S. Pat. No. 3,735,245 entitled "Method and Apparatus for Measuring Fat Content in Animal Tissue Either in Vivo or in Slaughtered and Prepared Form", invented by Wesley H. Harker, teaches that the fat content in meat can be determined by measuring the impedance difference between fat and meat tissue. The Harker apparatus determines gross impedance change and does not provide adequate spatial resolution for the present use. U.S. Pat. No. 4,240,445 teaches the use of an electromagnetic field responsive to the dielectric impedance of water to detect the presence of water in a patient's lungs. However, such an apparatus does not detect the conductivity variations required in the present invention. U.S. Pat. No. 3,789,834 relates to measurement of body impedance by using a transmitter and receiver and computing transmitted wave impedance from the electrical or magnetic field generated. However, the antenna pickup would receive extraneous noise rendering it inappropriate for the present use. None of the above-cited references contemplate measuring the loss of bone mass associated with osteoporosis by measuring the impedance of the bone and none of the references teach an apparatus capable of specifically detecting such impedance.